On new-years eve, 1966, the federal government (of the US) elected Boeing to design the nation's first SuperSonic Transport, or SST.
The amazing result was that 26 airlines placed orders for 122 ships, each being 318 feet long with four 60,000 pound thrust engines. The jet was designed to cruise at 60,000 feet at Mach 2.7.
In 1971 Congress voted down further funding for the project, before the prototype was completed. A full-scale model remains somewhere, in pieces. The original design would have had variable-geometry wings, but the final result was fixed delta-wing, like the Concorde.
Obviously, the jet never flew.

The Boeing 2707-300 metal mockup is in a scrapyard just south of the Kennedy Space Center in Florida. I happened upon it in while visiting there in October, 1998. It was in several large pieces, but was easily
identifiable. As far as I know, it's still there.

A bit like the Soviet Union, the USA also felt that they could not leave the field of Supersonic Air Transport to France and Britain. However, none of the US manufacturers were convinced that a market existed for such an aircraft. Consequently, none of them were willing to launch a programme without Government financial support. Rather than fund two or three potential rivals, the US government decided to evaluate three "paper" proposals from Boeing, McDonnell Douglas and Lockheed. Boeing came out on top with their proposal and they received the funding. Boeing's design was the most advanced, with a much larger aircraft than Concorde or the Tu-144 and a higher cruising speed. It also featured swing wings which were very much in vogue at the time.The first thing they built was the mock up referred to above. However, it was not long before the designers found that the swing wing option was almost a non-starter and so that aspect of the design was dropped to be replaced by a more conventional delta wing. This did not please Lockheed or McDonnell Douglas as their original rejected propsals had featured delta wing designs.

In the event, the strain on US government funds caused by the Vietnam War and the Apollo programme meant that funding was withdrawn in 1971. With no government money now available, Boeing shelved the whole project, probably with a great sigh of relief. The wooden mockup survived for many years as a tourist attraction in the Orlando area but now appears to be no more.